Enhanced fatigue resistance and lattice dynamics induced by the strong local strain in Fe-doped KTa1−xNbxO3 single crystals

Abstract

Improving the durability of lead-free-doped piezoelectric materials is very important for their practical application. However, the promotional mechanism of anti-fatigue properties and the impact on local structures of ion dopants should be further revealed. Here, we investigate the improvement of fatigue resistance in Fe-doped KTa_1−xNb_xO₃ single crystals and reveal the origin of enhanced anti-fatigue properties. Fe-doping gives rise to the promotion of strain (by more than two times) and large enhanced anti-fatigue properties (only an 11.5% drop after 10⁵ electric cycles). Furthermore, the dynamic evolution of doped lattices during the fatigue process is experimentally characterized. The lattice contraction and the stability of doped lattice vibration modes are demonstrated, leading to the stabilization of E_ib and the enhanced recoverability of domain structures. Moreover, HRTEM reveals that the restriction of oxygen vacancies and the stable lattice vibrations are improved via the strong local strain fields induced by lattice distortion, which is fundamentally responsible for the enhancement of the fatigue resistance. The study revealing the promotional origin of anti-fatigue provides an effective strategy to design the local strain fields by doping modification to optimize the properties of ferroelectrics, which is greatly significant in the practical application of lead-free ferroelectrics.